FIG. 6 is a sectional view illustrating a makeup of a conventional acceleration sensor. At a part close to diaphragm 20 on the top surface of chip 1 formed with diaphragm 2, strain-sensitive resistors 3 are provided. The other part of the top surface of chip 1 is provided with a semiconductor integrated circuit for calculating acceleration, and thin-film resistor 4 for adjusting the characteristic of the integrated circuit thereon. Further, at a part including at least the top part of thin-film resistor 4, but excluding the top part of strain-sensitive resistors 3, protective film 5 is formed. Applying acceleration causes weight 6 made of glass to become stressed, changing the resistance of strain-sensitive resistors 3. Measuring this change enables detecting acceleration. Such an acceleration sensor is disclosed, for example, in Japanese Patent Unexamined Publication No. H05-288771.
FIG. 7 is a block diagram illustrating a makeup of another conventional acceleration sensor. This acceleration sensor includes piezoelectric element 11 for outputting signals corresponding to acceleration; converter 12 for converting the impedance of output signals; filter 13 for removing unnecessary signals; and amplifier 14 for amplifying necessary signals. The sensor further includes alternating current (AC) signal output part 16 for outputting AC signals synchronized with the cycle of timing signals being externally input. Between AC signal output part 16 and piezoelectric element 1, capacitor 17 is connected in series. The voltage signals output from the acceleration sensor are to be introduced to measurement/operation unit 18 and controller 15, both equipped with a microprocessor. Such an acceleration sensor is disclosed, for example, in Japanese Patent Unexamined Publication No. H05-80075.
In the above-mentioned makeup, strain-sensitive resistor 3 or piezoelectric element 11 detects acceleration. In such a method of detecting acceleration by means of a strain of a semiconductor resistor, the resistance changes by only a few percent and fluctuates largely. Besides, the resistance is influenced by the change in temperature of the signal process circuit, disabling precise detection of acceleration.
In addition, it is presumably difficult to detect the component for such as static gravity acceleration due to the detection structure. In other words, a makeup for detecting a variation in speed by means of a strain of a semiconductor resistor is unable to detect acceleration due to such as static gravity.